Process for the production of unsaturated monocarboxylic acid esters



United States Patent Ofiice 3,022,338 Patented Feb. 20, 1962 PROCESS FORTHE PRODUCTIUN F UNSATU- RATED MONOCARBOXYLIC ACil ESTERS Eduard Enlrand Fritz Kniirr, Burghauseu, Upper Bavaria, Germany, assignors toWacker- Ihemie G.m.b.H.,

Munich, Germany No Drawing. Filed June 23, 1959, Ser. No. 822.213

Claims priority, application Germany June 25, 1958 I 8 Claims. (Cl.260-486) The present invention relates to an improved process for theproduction of unsaturated monocarboxylic acid esters from alphaorbeta-alkoxy or aryloxy substituted monocarboxylic acid esters employingmixed silica con- In the case of acrylic transition elements ascomplexly bound anions as, for

The production of alpha-beta unsaturated esters by splitting ofl?alcohol from beta-alkoxy substituted propionic or isobutyric acid estersin the liquid phase in the presence of sodium alcoholate has beendescribed in US. Patent No. 2,393,737. It has also been proposed toimprove the yields and increase the velocity of the reaction bydissolving the sodium methylate employed as the catalyst in methanol andto permit to drop the betamethoxy isobutyric acid methyl ester into theheated solution at the same rate as the methacrylic acid methyl esterwhich is formed distilis off. It was possible in this way to achieveyields of up to 92.5% based upon the betamethoxy isobutyric acid methylester converted. However, the separation of a large excess of methanolfrom the methacrylic acid methyl ester by extractive or azeotropicdistillation is rather costly.

In order to increase the velocity of the conversion,

the alkaline cleavage of beta-alkoxy substituted esters with theformation of alpha-beta unsaturated esters was carried out in the gasphase according to U.S. Patent No. 2,457,225 employing basic alkalimetal and alkaline earth metal compounds as catalysts. The cleavageproducts obtained are essentially free of acid but in view of the hightemperatures required for the dealcoholysis considerable decompositionof the ester formed occurred which is evidenced by the strong yellowbrown coloration of the cleavage product and the deposit of carbon onthe catalyst which reduced its activity.

According to the invention it was found that unsaturated monocarboxylicacid esters can be produced by dealcoholizing alphaor beta-alkoxy oraryloxy substituted monocarboxylic acid esters employing mixed catalystswhich in addition to alkaline earth metal phosphates, particularly theprimary phosphates of calcium and magnesium, also contain compounds ofthe transition elements of groups I to VIII of the periodic system(according Holleman-Wiberg, Lehrbuch der Anorganischen Chemie, 26 and 27edition, 1951, Verlag Walter de Gruyter n. Go, Berlin, pages 424 et.seq.). It. furthermore was found advantageous if such mixed catalystsare supported on carriers having a large surface area. Silica Y gel isparticularly suited as such a carrier but other carriers, such as activecarbon, pumice, silicates, such as kaolin, silica earths and the likecan also be employed.

It is advantageous when the alkaline earth metal phosphate constitutesthe major portion, preferably at least 70% by weight, of the mixedcatalyst. The compounds of the transition elements of groups I to VIIIof the periodic system which are to be used in conjunction with thephosphates can be oxides or salts of preferably the following elements:copper, silver, gold, cerium, zirconium, hafnium, thorium, vanadium,niobium, tantalum, chromium, molydenum, tungsten, uranium, iron, cobalt,nickel and the platinum metals. Salts of these metals can be employed inwhich such metals are cations, such as, for example, in halides,nitrates, nitrites, sulfides, sulfates, sulfites, phosphates, phosphitesor borates. However, such metal salts can be employed which contain theexample, in chromates, vanadates, tungstates, molybdenates and uranates.It is also possible to add mixtures of the above mentioned compounds oftransition elements to the alkaline earth metal phosphates. In addition,it is possible to add the transition elements themselves if they reactwith acid reacting phosphates or with added phosphoric acid or otheracids to produce metal salts. Mixed catalysts of alkaline earth metalphosphates with mixtures of the indicated types of compounds of thetransition elements can also be used. In some instances it can beadvantageous if small quantities of aluminum or boron compounds,especially the phosphates, are added to these mixtures.

The catalysts according to the invention are advantageously employed attemperatures between 250 and 380 (3., preferably between 300 and 350 C.The conversion according to the invention can be carried out in the gasor liquid phase and can be carried out continuously or discontinuously.When it is carried out in the gas phase, the vaporized material ispassed through a heated tube filled with the catalyst at atmospheric orsubatmo spheric pressure, preferably admixed with an inertgas, such asnitrogen. The heating of the catalyst tube can be effected by electricheating or with a heated gas which is passed over the tube with ablowerto prevent local overheating.

The vapors after the cleavage and condensation are collected in a trapcooled to about 0 C. and the unsaturated monocarboxylic acid esters areseparated from the non-converted starting material and by-products bysimple or azeotropic distillation. The components reaction mixture,however, also can be recovered by extractive distillation in a knownmanner, if desired, with the addition of shaking, spraying or vibration,or by chemical measures which favor the formation of large surfaceareas. Care must be taken that the reaction product is withdrawn fromthe reaction chamber as rapidly as possible. The use-of superatmosphericpressures promotes the reaction.

The degree of cleavage the ether esters attained in the processaccording to the invention depends upon the reaction temperature, aswell as the quantity of catalyst provided. The quantity of starting.material charged to the catalyst per unit of time can be varied withinwide limits and can be adapted to the conditions at hand.

Preferably, the alcohols from which the alkoxy and ester groups of thestarting alkoxy monocarboxylic acid esters are derived are alkanolscontaining 1 to 8 carbon atoms.

The following examples will serve to illustrate a numon silica gel.

3 Example 1 Beta-methoxy propionic acid methyl ester was passed in vaporform at 350 C. over a catalyst consisting of 30%- Example 2 Beta-methoxypropionic acid methyl ester was passed in vapor form at 350 C. over acatalyst which contained 30% of primary magnesium phosphate and 1% ofiron The iron was applied to the catalyst as iron (III) chloride. Therate at which such ether-ester was passed over the catalyst was 0.6 g.per cc. of catalyst per hour. The conversion was 86.6% with reference tothe ether-ester supplied to the catalyst. The yield of acrylic acidmethyl ester was 91.5% with reference to the ether-ester converted.

Example 3 Beta-methoxy isobutyric acid methyl ester was passed in vaporform at 330 C. over a catalyst consisting of 4 Example 6 500 cc. ofsilica gel of a grain size of 4-6 mm. was impregnated with an aqueoussolution containing 40 g.

of phosphoric acid (calculated as 100% 28.4 g. of magnesium chloridehexahydrate, 2.7 g. aluminum chloride hexahydrate and 1.1 g. of thoriumnitrate tetrahydrate.

, The catalyst was dried at 100 C. and then heated for 48 hours at 700C.

Beta-methoxy propionic acid methyl ester was passed over this catalystas in Example 5. The conversion was 81.1% with reference to theether-estersupplied to the catalyst and the yield of acrylic acid methylester was 92.7% with reference to the ether-ester converted.

We claim:

1. A process for the production of cop-unsaturated monocarboxylic acidesters which comprises contacting of primary magnesium phosphate, 2% ofcopper oxide and 1% of nickel oxide supported on silica gel. The rate atwhich such ether-ester was passed over the catalyst was 0.8 g. per cc.of catalyst per hour. The conversion was 87.6% with reference to theether-ester supplied to the catalyst. The yield of methyl methacrylatewas 90.3% with reference to the ether-ester converted.

Example 4 Beta-methoxy isobutyric acid methyl ester was passed as inExample 3 over a catalyst consisting of 30% of primary magnesiumphosphate, 1.5% of ammonium vanadate and 0.15% of cerium sulfatesupported on silica gel. The conversion was 82.5% with reference to theether-ester supplied to the catalyst. The yield of methyl methacrylatewas 92.4% with reference to the etherester converted.

Example 5 500 cc. of silica gel of a grain size of 4-6 mm. was

impregnated with an aqueous solution containing 48 g.

Beta-methoxy propionic acid methyl ester was passed in vapor form at 350C. over this catalyst at a velocity of 0.37 g. per cc. of catalyst perhour. The conversion was 87.0% with reference to the ether-estersupplied to the catalyst and the yield of acrylic acid methyl ester was94.2% with reference to the ether-ester converted.

a B-alkoxy monocarboxylic acid ester with a catalyst comprising analkaline earth metal phosphate and a compound of a transition element ofgroup I to group VIII of the periodic system selected from the groupconsisting of copper, cerium, thorium, vanadium, chromium, iron andnickel at a temperature between 250 and 380 C. to form ana,B-unsaturated carboxylic acid ester and an alcohol.

2. The process of claim 1 in which the quantity of alkaline earth metalphosphate in said mixed catalyst constitutes at least by weight of thecatalyst.

3. The process of claim 1 in which said catalyst additionally contains arelatively small quantity of an aluminum phosphate.

4. The process of claim 1 in which said catalyst additionally contains arelatively small quantity of a boron phosphate.

5. The process of claim 1 in which said mixed catalyst is supported on acarrier.

6. The process of claim 1 in which said mixed catalyst is supported onsilica gel.

7. The process of claim 1 in which said ,B-alkoxy monocarboxylic acidester is contacted with the catalyst at temperatures between 300 and 350C.

8. The process of claim 1 in which said B-alkoxy monocarboxylic acidester is a fl-alkoxy monocarboxylic acid alkyl ester.

References Cited in the file of this patent UNITED STATES PATENTS KungMay 22, 1945 Gresham Dec. 28, 1948 OTHER REFERENCES

1. A PROCESS FOR THE PRODUCTION OF A,B-UNSATURATED MONOCARBOXYLIC ACIDESTERS WHICH COMPRISES CONTACTING A B-ALKOXY MONOCARBOXYLIC ACID ESTERWITH A CATALYST COMPRISING AN ALKALINE EARTH METAL PHOSPHATE AND ACOMPOUND OF A TRANSITION ELEMENT OF GROUP I TO GROUP VIII OF THEPERIODIC SYSTEM SELECTED FROM THE GROUP CONSISTING OF COPPER, CERIUM,THORIUM, VANADIUM, CHROMIUM, ION AND NICKEL AT A TEMPERATURE BETWEEN 250AND 380* C. TO FORM AN A,B-UNSATURATED CARBOXYLIC ACID ESTER AND ANALCOHOL.